The present invention relates to a circuit for detecting breakage of a large number of heating members arranged to construct a thermal head.
When a heating member on a printer thermal head breaks, the heating member does not generate the correct amount of heat for printing, and a missing letter or line results therefrom. Previously, broken heating members were detected by observing the printed surface of a test sheet. However, this visual testing method could not detect every broken heating member, since some broken heating members were located at white portions of the document. Therefore, unless incorrect letters were printed, the abnormality of the heating member could not be detected, and satisfactorily prevented.
In addition, some testing methods uses a test pattern in which the sheet was partially colored throughout, thereby requiring partial heating of every member. This, test pattern arrangement often caused the power supply to be overloaded and damaged. Therefore, it was necessary to arrange the test pattern such that the power supply of the thermal head was not overloaded. Finally, the only proposed circuit for electrically detecting broken heating members is complicated and expensive, thereby making it unpractical.